If you're discharging a recently-used tube,
don't use a simple
resistor. The EHT on a CRT could be anything from 8kV to several tens
Indeed. COnsider several resistors in series -- 50 - 100 1M in series
would seem to be OK. A recomended way of mounting them is to 'wind' the
chain round a plastic strip. That way, points at very different votlages
are kept apart.
of kV in a fancy colour tube, and most common
resistors have a
breakdown voltage of only 500-1000V. Besides, think about the power
dissipation if you discharge a 25kV tube through a 10M resistor: 2.5
milliamps, but 62 watts. Sure, that 62W won't last long, but neither
the tube nor your resistor will like it!
Hmm.. I would be suprised if the capacitance of the average CRT was more
than 110pF (I've never measured it, though). Which, using E=1/2*C*V^2,
would give the stored energy as 31.25mJ at 25kV EHT. That is not going to
damage any normal resistor.
-tony